The present invention relates to a plasma treatment apparatus for applying plasma treatment to substrates such as semiconductor substrates as well as to an etching method using plasma.
For example, in a manufacturing process of semiconductor devices, plasma treatment, such as etching, sputtering, CVD (chemical vapor deposition) is popularly used for semiconductor wafers, to-be-treated substrates.
For plasma treatment apparatus to carry out this kind of plasma treatment, various types are available, and of them, the capacitive coupling type parallel flat plate plasma treatment apparatus is of the mainstream.
The capacitive coupling type parallel flat plate plasma treatment apparatus has a pair of parallel flat plate electrodes (upper and lower electrodes) arranged in the chamber, forms a high-frequency electric field between the electrodes by introducing process gas into the chamber and applying high frequency to one of the electrodes, and thus forms plasma of process gas by the high-frequency electric field to apply plasma treatment to the semiconductor wafer.
When a film on the semiconductor wafer, for example, an oxide film, is etched by the capacitive coupling type parallel flat plate plasma treatment apparatus, the optimum radical control is enabled by keeping the chamber inside to a medium pressure and forming a medium-density plasma, thereby attaining the optimum plasma condition as well as achieving etching of high stability and reproducibility at high selection ratio.
Specifically, it is disclosed in the 1997 Dry Process Symposium P385-390 that satisfactory etching is able to be achieved at 20 to 100 mTorr pressure by applying high frequency of 27.12 MHz for plasma forming to the upper electrode to form the plasma while applying high frequency of 800 kHz to the lower electrode to draw in ions generated by plasma.
However, in recent years, refinement of the design rule in USLI has still more increased and a still higher aspect ratio of the hole profile is required, and conventional conditions are not always able to satisfy oxide film etching, etc.
It is an object of the present invention to provide a plasma treatment apparatus that can respond to the increased refinement and an etching method that can achieve etching satisfying requirements of increased refinement and with higher selectivity.
According to the first aspect of the present invention, there is provided a plasma treatment apparatus for generating plasma of a process gas by forming a high-frequency electric field between first and second electrodes while introducing the process gas into a chamber held to reduced pressure with the first and the second electrodes mounted opposite to each other inside the chamber and with the to-be-treated substrate supported by the second electrode, and applying a specified plasma treatment to the to-be-treated substrate with this plasma, in which the first high-frequency power supply with the frequency in the range from 50 to 150 MHz is connected to the first electrode, and the second high-frequency power supply with the frequency in the range from 1 to 4 MHz is connected to the second electrode.
According to the second aspect of the present invention, there is provided an etching method for etching an SiO2 film formed on an SiN film on a substrate with plasma of process gas contains C4F8 which is formed by a high-frequency electric field applied between first and second electrodes while introducing the process gas into a chamber held to reduced pressure with the first and the second electrodes mounted opposite to each other inside the chamber and with the to-be-treated substrate supported by the second electrode, the improvement in which the high frequency in the range from 50 to 150 MHz is applied to the first electrode and a high frequency in the range from 1 to 4 MHz is applied to the second electrode.
In the present invention, when a high-frequency electric field is formed between the first and the second electrodes to generate plasma of the process gas while the process gas is being introduced into the chamber held to reduced pressure, and plasma treatment, particularly, etching treatment, is carried out on the to-be-treated substrate by the plasma with the first and the second electrodes mounted opposite to each other in the chamber and the to-be-treated substrate supported by the second electrode, high frequency of 50 to 150 MHz is applied to the first electrode and high frequency of 1 to 4 MHz is applied to the second electrode, both of which are higher than the conventional. Because by applying high frequency of 50 to 150 MHz to the first electrode, which is higher than the conventional, in this way, it is possible to increase the plasma density without changing the plasma dissociation condition from that of the conventional suitable plasma, and to form the suitable plasma in still lower pressure condition, it is possible to properly respond further advanced refinement of design rule. In addition, it is possible to exert suitable ion effects on the to-be-treated substrate at low pressure by applying high frequency of 1 to 4 MHz to the second electrode, which is higher than-the conventional, and particularly in the case of etching, anisotropic etching with still higher selectivity becomes possible, and at the same time, damage to the to-be-treated substrate decreases. In-addition, it is also possible to achieve plasma treatment, particularly, etching treatment, with a wide margin of process conditions and extremely high stability by adopting the conditions of the present invention.
In this case, it is desirable that the high frequency applied to the first electrode ranges from 50 to 80 MHz and the high frequency applied to the second electrode ranges from 1 to 3 MHz. Typically, the high frequency applied to the first electrode is about 60 MHz and the high frequency applied to the second electrode is about 2 MHz. When etching is carried out in this way, it is desirable to keep the chamber inner pressure at 1.06 to 13.3 Pa.
The etching method according to the present invention is effective when the to-be-treated substrate has an SiN film and an SiO2 film thereon and an etched layer is SiO2 film, and for the process gas in such a case, that containing C5F8 and O2 is suitable. In this case, noble gas such as Ar or He, or N2 may be added in addition to C5F8 and O2. Or, other fluorocarbon gas (CxFy) such as CF4, C4F8 or hydrofluorocarbon gas (CpHqFr) such as CHF3, CH2F2 may be added. The partial pressure of C5F8 is preferably between 0.5 mTorr and 2 mTorr. In addition, in the process gas containing C5F8 and O2, the flow ratio O2/C5F8 of C5F8 to O2 is preferable to be in the range of ⅝xe2x89xa6O2/C5F8xe2x89xa6xe2x85x9e.
Similarly, when the to-be-treated substrate has the SiN film and SiO2 film thereon and the etched layer is the SiO2 film, the process gas containing C4F8 is also suitable. In such case, noble gas such as Ar, He or N2 may be added in addition to C4F8. Or, in the similar manner, other fluorocarbon gas or hydrofluorocarbon gas may be added. Since satisfactory etching characteristics are able to be obtained at the pressure inside the chamber as low as 1.06 to 2.00 Pa when the gas containing C4F8 is used for the process gas, it is desirable to carry out etching at such low pressure. In addition, when a hole is formed in the SiO2 film by etching in this way, properly controlling the conditions enables etching at a high etch rate even when the hole diameter is as fine as 0.1 to 0.4 xcexcm. In particular, 0.15 to 0.4 xcexcm is desirable.